Fixed Wing Angle eVTOL
Aerospace
Fixed Wing Angle eVTOL (LAR-TOPS-338)
VTOL Without Performance Limitations
Overview
Current electric vertical takeoff and landing aircraft (eVTOL) configurations for Urban Air Mobility (UAM) applications often require performance-hindering equipment only used for a specific operation (e.g., takeoff or cruising). The need for such equipment, such as separate lift and thrust mechanisms, often stems from the challenge posed by transitioning from hovering to forward flight. For example, tilt-wing eVTOLs have complex transition periods that can result in large pitching movements or wing stalling without adequate propulsion, potentially causing catastrophic loss of control. Increased equipment requirements for eVTOLs also increase system mass, negatively impacting performance.
Innovators at NASA's Langley Research Center recognized this issue and have developed a novel eVTOL solution design. The technology is a distributed electric propulsion, modular wing aircraft capable of vertical takeoff and landing, without requiring near 90° wing tilt. Instead, NASA's eVTOL uses large flaps and a fixed slight wing tilt to generate upward force, enabling VTOL operations, benign transition from hovering to forward flight, and increased safety and simplicity of operations.
The Technology
While previous eVTOLs often require a near 90° wing tilt to position propellers in an optimal location to generate vertical force for takeoff, NASA has taken a very different approach. NASA's design instead uses a slight wing angle and large flaps designed to deflect slipstream generated by the propellers to create a net positive force in the vertical direction, all while preventing forward movement. This unique configuration allows for takeoff and landing operations without the need for near 90° wing tilt angles. After takeoff, the transition to forward flight only requires a slight change in attitude of the vehicle and retraction of the flaps. Similar solutions require large changes in attitude to accomplish this transition which is often undesirable, especially for air taxi operations that involve passengers.
Given the effectiveness of this configuration for generating upward force, the requirement for wing angle tilt has been reduced from near 90° to approximately 15° during takeoff. Further iterations may reduce this requirement even further to 0°. By eliminating the need for near 90° wing tilt, NASA's eVTOL design removes the need for mechanisms to perform active tilting of the wings or rotors, reducing system mass and thereby improving performance. Flaps represent the only components that require actuation for takeoff and landing operations.
Innovators at NASA leveraged the Langley Aerodrome 8 (LA-8), a modular testbed vehicle that allows for rapid prototyping and testing of eVTOLs with various configurations, to design and test this novel concept.
Benefits
- Eliminated performance-hindering equipment: Removing the need for active wing angle actuation reduces hardware requirements, resulting in decreased mass and increased performance
- Smooth transition operations: Enables benign transition from hovering to forward flight (only requires a small attitude change) - ideal for air taxi applications
- Increased operational simplicity: Eliminates the need for mechanisms to manipulate wing angles during transitions from takeoff to forward flight
Applications
- Urban air mobility: eVTOL passenger vehicles for air taxi services
- Drone delivery: eVTOL delivery vehicles
- Industrial applications: eVTOL vehicles are being considered for use in various industries including agriculture and construction
Technology Details
Aerospace
LAR-TOPS-338
LAR-19644-1
LAR-18332-1
LAR-18332-1-CON
“An Experimental Approach to a Rapid Propulsion and Aeronautics Concept Testbed,” McSwain, Robert et. al., January 1, 2020,
https://ntrs.nasa.gov/citations/20200000698
https://ntrs.nasa.gov/citations/20200000698
Similar Results
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The Active Turbulence Suppression (ATS) system for electric Vertical Take-Off and Landing (eVTOL) vehicles employ existing lifting propellers to dampen instabilities during flight, such as Dutch-roll oscillations and other gust-induced oscillations. When a roll angle of an eVTOL aircraft has deviated or is about to deviate from a current stable aircraft state to an undesirable, unstable, and oscillating aircraft state, the ATS system queries a turbulence suppression database that stores a set of propeller speed profiles for mitigation a deviation of a given roll angle for a particular aircraft with specified propellers. Using this data, the eVTOL flight controller adjusts the speed of the propellers for a certain duration of time, according to the propeller speed profiles for mitigating the deviation. In models of aircraft with adjustable propeller angles, the database includes blade angle profiles for mitigating the effects of turbulent conditions. Timing and rate of propeller activation can be pre-computed using higher order computational modeling performed with NASA’s super computing resources. Because the data is pre-computed, the use of the ATS system onboard does not require significant computing resources to implement on eVTOL vehicles. The technology, a mechanism by which existing eVTOL propellers are leveraged to suppress gust-induced oscillations enables a safe and comfortable passenger experience at low-cost and without added hardware.
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In a test of the wind-optimal airspeed targeting technique using a multi-rotor aircraft model, results obtained show benefits of flying at the wind‐optimal cruise airspeed compared to the best‐range airspeed. In headwind conditions, energy consumption was reduced by up to 7.5%, and flight duration was reduced by up to 28%. Under uncertain wind magnitudes, flying at wind-optimal airspeed offered lower variability and higher predictability in energy consumption than flying at best‐range airspeed.
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